The present invention relates to a pneumatic tire with a wide groove such as central wide circumferential groove, more particularly to a small rib arrangement in the wide groove being capable of preventing occurrence of bareness of tread rubber in the groove bottom.
In general, a tire mold (d) in which pneumatic tires are vulcanized is, as shown in FIG. 10, provided with vent holes (f) to remove air between the mold (d) and the tire (c). If air is not fully removed, so called bareness of rubber occurs. Due to the vent holes (f), spues or pips of rubber are inevitably formed on the vulcanized tire. Usually the spues are cut off before shipping. If spues are formed in tread grooves, it is hard to cut off the spues. Therefore, vent holes (f) usually avoid the groove wall and bottom.
In recent years, on the other hand, a wide circumferential groove (i) disposed in the tread center is employed even in relatively small size tires such as passenger car tires in order to improve wet performance especially antiaquaplaning performance, running noise and the like. In such case, bareness (j) of tread rubber is liable occur in the bottom of the wide circumferential groove (i).
It is therefore, an object of the present invention to provide a pneumatic tire with a wide groove, in which bareness of tread rubber in the groove bottom is effectively prevented.
According to one aspect of the present invention, a pneumatic tire comprises a wide groove having a bottom width of not less than 20 mm disposed in a tread portion, the wide groove provided on the groove bottom with at least one longitudinal rib extending in the longitudinal direction of the wide groove, and lateral ribs extending from the longitudinal rib towards a tread face through the groove bottom and a groove wall of the wide groove.
Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings.
FIG. 1 is a developed plan view of a pneumatic tire according to the present invention.
FIG. 2 is a perspective view of the tread portion thereof wherein spues remain in the tread surface.
FIG. 3 is an enlarged sectional view of the wide groove taken along a line Axe2x80x94A of FIG. 1.
FIG. 4 is a cross sectional view of the longitudinal rib.
FIG. 5 is a cross sectional view of the intermediate rib.
FIG. 6 is a cross sectional view of the lateral rib.
FIGS. 7A, 7B, 7C and 7D are schematic plan views each showing another example of the intermediate rib arrangement.
FIG. 8 is a diagram for explaining a tire mold.
FIG. 9 is a partial perspective view of the tire mold showing a part corresponding with the wide groove shown in FIG. 2.
FIG. 10 is a cross sectional view for explaining bareness of tread rubber in the groove bottom of a wide circumferential groove.